1. Field of the Invention
The present invention relates to a radiographic apparatus for obtaining a radiographic image of a subject by irradiating the subject with a radiation such as X-ray.
2. Related Background Art
The radiographic apparatus is utilized in the medical field for example for medial diagnosis of an inspected person and in the inspection field for example for non-destructive inspection of a material, and there are some types of the image receiver for receiving the radiographic image.
A first method is the photoradiographic method in which a sensitizing sheet and a photoradiographic film are used in mutual contact. In this method, when the radiation transmitted through an object enters the sensitizing sheet, a phosphor contained therein absorbs the energy of the radiation to generates fluorescence, the photoradiographic film is exposed by the fluorescence, and the radiographic image is reproduced as a visible image by developing the photoradiographic film.
A second method utilizes an image recording/reproducing apparatus provided with a radiation image detector composed of a photostimulable phosphor. When the radiation transmitted through an object enters the photostimulable phosphor, it accumulates a part of the radiation energy. Then, when the photostimulable phosphor is irradiated with visible light, the photostimulable phosphor generates an accelerated phosphorescence emission corresponding to the accumulated energy. Thus, the photostimulable phosphor accumulates the radiation image information of the object, then scanning means scans the photostimulable phosphor with excitation light such as laser light, and signal reading means photoelectrically reads the accelerated phosphorescence emission whereby the radiation image is recorded or displayed as a visible image by recording means such as a printer utilizing a recording material such as a photographic material, or by display means such as a cathode ray tube (CRT).
A third method utilizes a radiation image detector capable of detecting the radiation image on real-time basis and directly outputting a digital signal. The principle of such detector is described for example in the Japanese Patent Application Laid-Open No. 8-116044. Such digital detector has been enabled by the progress of the semiconductor technology, and comprises a scintillator and solid-state light detector which are formed in a laminated structure and in which the scintillator converts the radiation into visible light and the solid-state light detector executes photoelectric conversion of the visible light. The solid-state light detector is composed, on a quartz glass substrate, of a matrix array of solid-state light detecting elements each composed of an amorphous semiconductor film sandwiched between a transparent electroconductive film and an electroconductive film. As such radiation detector can be formed as a flat panel of a thickness of several millimeters, the image receiver can be easily made thin and light.
FIG. 1 shows an example of the configuration of the apparatus, with a bucky radiographic table to be used in the plain radiography of extremities, head, abdomen etc. of a subject S, seen in the longitudinal direction (from above the head of the subject). In such apparatus, the subject S lying on a top plate 1 is irradiated by the X-ray from a tube T positioned above, and the X-ray transmitted through the subject S is received by the radiographic image receiver 2 to obtain the radiation image.
In the medical practice sites, it is desired to obtain the images of the object from various direction with simple operations, and there is provided an apparatus shown in FIG. 2 for meeting such requirement. In such apparatus, in order to take the image on the lateral side of the subject S on the top plate 1, a cassette 3 containing a film or a photostimulable phosphor sheet is placed at a side of the subject S while the X-ray is irradiated from a lateral tube T′ whereby the X-ray image transmitted through the subject S is received by the film or the photostimulable phosphor sheet in the cassette 3.
It is however desirable, if possible, to use a same image receiver in image taking from any direction, without deteriorating the safety or operability.